Development of Machine-to-Machine Communication has been progressed that is for achieving autonomous communication between terminals without intervention of human operation. The machine-to-machine communication in the Third Generation Partnership Project (3GPP) has been referred to as Machine Type Communication (MTC). In the 3GPP Rel. 11, a network optimization function for an MTC terminal is studied. In the 3GPP Rel. 12, enhancement of coverage against building entrance loss is studied.
The enhancement of coverage may be required for a Shared channel (SCH), a Physical Broadcast Channel (PBCH), a Physical Random Access Channel (PRACH), a Physical Downlink Control Channel (PDCCH)/an Enhanced PDCCH (EPDCCH), a Physical Downlink Shared Channel (PDSCH), a Physical Uplink Shared Channel (PUSCH), a Physical Uplink Control Channel (PUCCH), and so forth.
There are various types of MTC terminals including an MTC terminal that can periodically transmit data, such as a gas meter, an electricity meter, and a temperature/humidity sensor; and an MTC terminal that can transmit data in response to occurrence of a specific event. It can be particularly important to enhance coverage, so that each terminal can quickly establish a radio link, regardless of a type of the MTC terminal and a location and/or an environment in which the MTC terminal is located.
In order to enhance coverage, same information can be repeatedly transmitted in a time domain. For example, for a PUCCH, an Automatic Repeat Request (ARQ) has been adopted that is for repeatedly transmitting the same data frame up to a predetermined number of times, after transmitting a data frame from a transmitting side and upon determining that no “ACK” can be received after a predetermined time has elapsed; and a Hybrid ARQ has been adopted that is combined with an error correction method (cf. Non-Patent Document 1, for example). Additionally, it has been proposed to transmit, through a PRACH, a preamble format for a long sequence (cf. Non-Patent Document 2, for example). It has also been known to apply the Hybrid ARQ to a part of a random access procedure.
Further, for enhancing coverage of a PDCCH, same information may be required to be repeatedly transmitted over a plurality of subframes.
Accordingly, a technique of compact DCI has been disclosed (cf. Patent Document 1, for example) such that a bit length of Downlink Control Information (DCI) that can be transmitted through a PDCCH is shortened. FIG. 1 is a conceptual diagram illustrating a concept of the compact DCI. As shown in FIG. 1, the compact DCI can have a structure such that a shortened CRC is attached to the compact DCI, so that the bit length of the DCI and the bit length of a Cyclic Redundancy Check (CRC), which is one of error detection codes to be attached to the DCI, can be shortened. In this manner, the coverage can be enhanced by repeatedly transmitting the DCI because the bit length of the compact DCI can be less than that of a usual one (normal DCI).    Patent Document 1: WO 2013/074722    Non-Patent Document 1: 3GPP TS36.213, 10.1.4 HARQ-ACK Repetition    Non-Patent Document 2: 3GPP TS36.211, 5.7 Physical random access channel    Non-Patent Document 3: 3GPP TS 36.212, 5.3.3 Downlink control information